The invention relates to an arrangement for the biological cleaning of water, which is particularly suitable for large urban cleaning stations or for the cleaning of waste water for industrial plants. The arrangement comprises an activating system with pneumatic aeration and with a supply of raw water and a separating system communicating therewith; the arrangement operates on the basis of fluid filtration, with an automatic return of activated sludge into the activating system and with the removal of cleaned water.
Biological activation, separation of activated sludge, and the return of a part of the activated sludge into the activation zone are generally used for the biological activation of waste waters. Arrangements operating on this principle apply a separated activation and separation; the separation is accomplished by sedimentation and return of the activated sludge by pumping. In small and medium cleaning stations of waste waters these arrangements are replaced by substantially more effective arrangements, in which separation of the activated sludge is accomplished by fluid filtration and the return of the activated sludge into the activation proceeds automatically by gravitation. Known arrangements of this kind are, however, limited in their size by their disposition and construction. Large cleaning stations of waste waters, for instance of fecal waters for outputs of the order above 10.sup.3 equivalent inhabitants, are at present built as classical arrangements. The common drawbacks of classical arrangements are a large floor space and volume of special sedimentation containers, their demanding machinery, and their complicated interconnection. These factors thereafter reflect unfavorably in investment costs and the demands for floor space for large cleaning stations of waste water.